Press

Claim 2

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, the upper platen and the center platen cooperating to define an upper workspace adapted to receive objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, the lower platen and the center platen cooperating to define a lower workspace adapted to receive objects to be pressed; e. platen support means movably supporting the upper and the lower platen from the framework, the support means including an upper sprocket wheel above the upper movable platen; a lower sprocket wheel below the lower movable platen; and an endless chain engaging the sprocket wheels and secured to the upper and lower movable platens, so that the weight of the upper platen is substantially balanced by the weight of the lower platen; and f. drive means for simultaneously forcing the upper platen down and the lower platen up toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens.

Claim 3

The improvement according to claim 1 wherein the drive means includes a motor coupled to the upper sprocket wheel for moving the movable platens toward the center platen, and hydraulic means secured to the framework and coupled to each movable platen, the hydraulic means being operable independently of the motor for moving the movable platens toward the center platen.

Claim 4

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate movable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. means for supporting the upper and lower movable platens from the framework, the support means including a first upper sprocket wheel mounted for rotation above the upper movable platen, a first lower sprocket wheel mounted for rotation below the lower movable platen, and a first endless chain engaging the first sprocket wheels and secured to the upper and lower movable platens so that the weight of the upper platen is substantially balanced by the weight of the lower platen; f. means for supporting the upper and lower intermediate movable platens from the framework, the support means including a second upper sprocket wheel having a diameter less than that of the first upper sprocket wheel adapted to rotate with said first upper sprocket wheel, a second lower sprocket wheel having a diameter less than that of the first lower sprocket wheel adapted to rotate with said first lower sprocket wheel, and a second endless chain engaging the second sprocket wheels and secured to the upper and lower intermediate movable platens so that the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen; and g. drive means for simultaneously forcing the upper platens down and the lower platens up toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens.

Claim 5

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate movable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. means for supporting the upper and lower movable platens from the framework, the support means including a first upper sprocket wheel mounted for rotation above the upper movable platen, a first lower sprocket wheel mounted for rotation below the lower movable platen, and a first endless chain engaging the first sprocket wheels and secured to the upper and lower movable platens so that the weight of the upper platen is substantially balanced by the weight of the lower platen; f. means for supporting the upper and lower intermediate movable platens from the framework, the support means including a second upper sprocket wheel having a diameter less than that of the first upper sprocket wheel adapted to rotate with said first upper sprocket wheel, a second lower sprocket wheel having a diameter less than that of the first lower sprocket wheel adapted to rotate with said first lower sprocket wheel, and a second endless chain engaging the second sprocket wheels and secured to the upper and lower intermediate movable platens so that the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen; and g. drive means for simultaneously forcing the upper platens down and the lower platens up toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens.

Claim 6

The improvement according to claim 12 in which the drive means includes a substantially horizontally disposed endless chain engaged with the front pair of sprocket wheels, and a separate horizontally disposed endless chain engaged with the rear pair of sprocket wheels, whereby the horizontal endless chains are useful in maintaining horizontal alignment of the movable platens during operation of the drive means.

Claim 7

The improvement according to claim 3 wherein the drive means includes a motor coupled to the upper sprocket wheels for moving the movable platens toward the center platen, and hydraulic means secured to the framework and coupled to the upper and lower movable platens, the hydraulic means being operable independently of the motor for moving the movable platens toward the center platens.

Claim 8

The improvement according to claim 1 including means for heating the center platen and the movable platens to substantially equal temperatures so that heat is uniformly applied to the objects in the workspaces.

Claim 9

The improvement according to claim 1 wherein the platen support means includes a second upper sprocket wheel above the upper movable platen and spaced laterally from the other upper sprocket wheel; a second lower sprocket wheel below the lower movable platen and spaced laterally from the other lower sprocket wheel; and an endless chain coupled with the upper sprocket wheels for use in maintaining horizontal alignment of the movable platens during operation of the drive means.

Claim 10

The improvement according to claim 3 including means for heating the center platen and the movable platens to substantially equal temperatures so that the heat is uniformly applied to the objects in the workspaces.

Claim 11

The improvement according to claim 3 including a third upper sprocket wheel mounted for rotation above the upper movable plAten and spaced laterally from the first upper sprocket wheel; a third lower sprocket wheel mounted for rotation below the lower movable platen and spaced laterally from the first lower sprocket wheel; a third endless chain engaging the third sprocket wheels and secured to the upper and lower movable platens so that the weight of the upper platen is substantially balanced by the weight of the lower platen; a fourth upper sprocket wheel having a diameter less than that of the third upper sprocket wheel adapted to rotate with said third upper sprocket wheel; a fourth lower sprocket wheel having a diameter less than that of the third lower sprocket wheel and adapted to rotate with said third lower sprocket wheel; a fourth endless chain engaging the fourth sprocket wheels and secured to the upper and lower intermediate movable platens so that the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen; and an endless chain coupled with the first and second upper sprocket wheels on the one hand and the third and fourth upper sprocket wheels on the other hand for use in maintaining horizontal alignment of the movable platens during operation of the drive means.

Claim 12

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate movable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. means for movably supporting the upper and lower movable platens from the framework so that the weight of the upper movable platen is substantially balanced by the weight of the lower movable platen, the support means including a first sprocket wheel rotatably mounted above the upper movable platen, and a chain engaging the sprocket wheel and secured at one end to the upper movable platen and at the other end to the lower movable platen; f. means for movably supporting the upper and lower intermediate movable platens from the framework so that the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen, the support means including a second sprocket wheel rotatably mounted above the upper movable platen such that it rotates independently of the first sprocket wheel, and a second chain engaging the second sprocket wheel and secured at one end to the upper intermediate platen and at its other end to the lower intermediate platen; and g. drive means for moving the pair of upper and lower movable platens on the one hand and the intermediate platens on the other hand toward the center platen in sequence to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens.

Claim 13

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate movable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. means for movably supporting the upper and lower movable platens from the framework so that the weight of the upper movable platen is substantially balanced by the weight of the lower movable platen, the support means including a first sprocket wheel rotatably mounted above the upper movable platen, and a chain engaging the sprocket wheel and secured at one end to the upper movable platen and at the other end to the lower movable platen; f. means for movably supporting the upper and lower intermediate movable platens from the framework so that the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen, the support means including a second sprocket wheel rotatably mounted above the upper movable platen such that it rotates independently of the first sprocket wheel, and a second chain engaging the second sprocket wheel and secured at one end to the upper intermediate platen and at its other end to the lower intermediate platen; and g. drive means for moving the pair of upper and lower movable platens on the one hand and the intermediate platens on the other hand toward the center platen in sequence to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens.

Claim 14

The improvement according to claim 8 wherein the drive means is adapted to move the upper and lower platens away from the center platen after applying pressure to the objects in the workspaces; and including lifting means secured to the upper platen for moving the upper intermediate platen away from the center platen as the drive means moves the upper platen away from the center platen.

Claim 15

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework anD having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, the upper platen and the center platen cooperating to define an upper workspace adapted to receive objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, the lower platen and the center platen cooperating to define a lower workspace adapted to receive objects to be pressed; e. platen support means for movably supporting the upper and lower platens from the framework so that the weight of the upper platen is substantially balanced by the weight of the lower platen, the platen support means including a first sprocket wheel rotatably mounted above the upper movable platen, a chain engaging the first sprocket wheel and secured at one end to the upper movable platen and at the other end at the lower movable platen, a second sprocket wheel rotatably mounted above the upper movable platen and spaced laterally from the first sprocket wheel, a chain engaging the second sprocket wheel and secured at one end to the upper movable platen and at the other end at the lower movable platen, and a substantially horizontally disposed endless chain engaged with the first and second sprocket wheels; and f. drive means for simultaneously forcing the upper platen down and the lower platen up toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens, the horizontal endless chain being useful in maintaining horizontal alignment of the movable platens during operation of the drive means.

Claim 16

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework anD having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, the upper platen and the center platen cooperating to define an upper workspace adapted to receive objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, the lower platen and the center platen cooperating to define a lower workspace adapted to receive objects to be pressed; e. platen support means for movably supporting the upper and lower platens from the framework so that the weight of the upper platen is substantially balanced by the weight of the lower platen, the platen support means including a first sprocket wheel rotatably mounted above the upper movable platen, a chain engaging the first sprocket wheel and secured at one end to the upper movable platen and at the other end at the lower movable platen, a second sprocket wheel rotatably mounted above the upper movable platen and spaced laterally from the first sprocket wheel, a chain engaging the second sprocket wheel and secured at one end to the upper movable platen and at the other end at the lower movable platen, and a substantially horizontally disposed endless chain engaged with the first and second sprocket wheels; and f. drive means for simultaneously forcing the upper platen down and the lower platen up toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens, the horizontal endless chain being useful in maintaining horizontal alignment of the movable platens during operation of the drive means.

Claim 17

An improved press comprising: a. a supporting framework having a front side and a rear side; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, the upper platen and the center platen cooperating to define an upper workspace adapted to receive objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, the lower platen and the center platen cooperating to define a lower workspace adapted to receive objects to be pressed; e. platen support means for movably supporting the upper and lower platens from the framework so that the weight of the upper platen is substantially balanced by the weight of the lower platen, the platen support means including a pair of laterally spaced apart front sprocket wheels on the front side of the framework above the upper movable platen, a pair of laterally spaced apart rear sprocket wheels on the rear side of the framework above the upper movable platen; a separate chain engaged with each front sprocket wheel and secured at one point to the upper movable platen and at another point to the lower movable platen; a separate rear chain engaged with each rear sprocket wheel and secured at one point to the upper movable platen and at another point to the lower movable platen; and f. drive means for simultaneously forcing the upper platen down and the lower platen up toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens.

Claim 18

An improved press comprising: a. a supporting framework having a front side and a rear side; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, the upper platen and the center platen cooperating to define an upper workspace adapted to receive objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, the lower platen and the center platen cooperating to define a lower workspace adapted to receive objects to be pressed; e. platen support means for movably supporting the upper and lower platens from the framework so that the weight of the upper platen is substantially balanced by the weight of the lower platen, the platen support means including a pair of laterally spaced apart front sprocket wheels on the front side of the framework above the upper movable platen, a pair of laterally spaced apart rear sprocket wheels on the rear side of the framework above the upper movable platen; a separate chain engaged with each front sprocket wheel and secured at one point to the upper movable platen and at another point to the lower movable platen; a separate rear chain engaged with each rear sprocket wheel and secured at one point to the upper movable platen and at another point to the lower movable platen; and f. drive means for simultaneously forcing the upper platen down and the lower platen up toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces, irrespective of the weight of the movable platens.

Claim 19

The improvement according to claim 13 in which one front sprocket wheel is aligned longitudinally with a respective one of the rear sprockeT wheels, and the other front sprocket wheel is aligned longitudinally with the remaining rear sprocket wheel; and including a pair of elongated rotatable shafts coupling the aligned pairs of front and rear sprocket wheels.

Claim 20

The improvement according to claim 14 including a drive motor coupled to at least one of said shafts for rotating said shaft and said front and rear sprocket wheels to drive the movable platens toward the center platen.

Claim 21

The improvement according to claim 15 including hydraulic means secured to the framework and coupled to each movable platen, the hydraulic means being operable independently of the motor for driving the movable platens toward the center platen.

Claim 22

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate movable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. platen support means for movably supporting the movable platens from the framework so that the weight of the upper movable platen is substantially balanced by the weight of the lower movable platen, and the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen; and f. drive means adapted to force the upper and lower movable platens and the intermediate movable platens toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces irrespective of the weight of the movable platens, the drive means including means for permitting the intermediate movable platens to move toward and away from the center platen independently of the upper and lower movable platens, so as to provide enlarged upper and lower workspaces within the press.

Claim 23

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate movable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. platen support means for movably supporting the movable platens from the framework so that the weight of the upper movable platen is substantially balanced by the weight of the lower movable platen, and the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen; and f. drive means adapted to force the upper and lower movable platens and the intermediate movable platens toward the center platen to apply substantially the same pressure to the objects disposed within the workspaces irrespective of the weight of the movable platens, the drive means including means for permitting the intermediate movable platens to move toward and away from the center platen independently of the upper and lower movable platens, so as to provide enlarged upper and lower workspaces within the press.

Claim 24

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate moveable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. first and second support means for movably supporting the upper and lower movable platens, and the intermediate movable platens, respectively, from the framework so that the weight of the upper movable platen is substantially balanced by the weight of the lower platen, and the weight of the upper intermediate movable platen is substantially balanced by the weight of the lower movable intermediate platen; and f. adjustable drive means either for forcing the intermediate movable platens toward the center platen at the same rate of speed as the upper and lower movable platens, or for forciNg the intermediate movable platens toward the center platen at a lower rate of speed than the upper and lower movable platens to provide either a two-opening press or a four-opening press, respectively, to apply substantially the same pressure to the objects disposed within the openings of the press, irrespective of the weight of the movable platens.

Claim 25

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate moveable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. first and second support means for movably supporting the upper and lower movable platens, and the intermediate movable platens, respectively, from the framework so that the weight of the upper movable platen is substantially balanced by the weight of the lower platen, and the weight of the upper intermediate movable platen is substantially balanced by the weight of the lower movable intermediate platen; and f. adjustable drive means either for forcing the intermediate movable platens toward the center platen at the same rate of speed as the upper and lower movable platens, or for forciNg the intermediate movable platens toward the center platen at a lower rate of speed than the upper and lower movable platens to provide either a two-opening press or a four-opening press, respectively, to apply substantially the same pressure to the objects disposed within the openings of the press, irrespective of the weight of the movable platens.

Claim 26

The improvement according to claim 18 in which the first platen support means includes a first upper sprocket wheel mounted for rotation about the upper movable platen, a first lower sprocket wheel mounted for rotation below the lower movable platen, a first endless chain engaging the first sprocket wheels and secured to the upper and lower movable platens so that the weight of the upper platen is substantially balanced by the weight of the lower platen; and wherein the second platen support means includes a second upper sprocket wheel having a diameter less than that of the first sprocket wheel, the second upper sprocket wheel being adapted to rotate with said first upper sprocket wheel, a second lower sprocket wheel having a diameter less than that of the first lower sprocket wheel, the second lower sprocket wheel being adapted to rotate with said first lower sprocket wheel, and a second endless chain engaging the second sprocket wheels and secured to the upper and lower intermediate platens so that the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen; and in which the adjustable drive means includes clutch means adapted to adjust the relative rates of rotation of the first and second sprocket wheels.

Claim 27

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate movable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. means for supporting the upper and lower movable platens from the framework, the support means including a first upper sprocket wheel mounted for rotation above the upper movable platen, a first lower sprocket wheel mounted for rotation below the lower movable platen, and a first endless chain engaging the first sprocket wheels and secured to the upper and lower movable platens so that the weight of the upper platen is substantially balanced by the weight of the lower platen; f. means for supporting the upper and lower intermediate movable platens from the framework, the support means including a second upper sprocket wheel having a diameter less than that of the first sprocket wheel and adapted to rotate independently of said first sprocket wheel, a second lower sprocket wheel having a diameter less than that of the first lower sprocket wheel and adapted to rotate independently of said first lower sprocket wheel, and a second endless chain engaging the second sprocket wheels and secured to the upper and lower intermediate movable platens so that the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen; and g. drive means for forcing the upper and lower movable platens and the intermediate platen toward the center platen in sequence to apply substantially the same pressure to objects disposed within the workspaces, irrespective of the weight of the movable platens.

Claim 28

An improved press comprising: a. a supporting framework; b. a substantially horizontal stationary center platen secured to the framework and having an upper surface and a lower surface; c. an upper movable platen disposed substantially parallel to the upper surface of the center platen, and an upper intermediate movable platen disposed between and substantially parallel to the center platen and the upper movable platen; the upper movable platens cooperating with the center platen to define a pair of upper workspaces for objects to be pressed; d. a lower movable platen disposed substantially parallel to the lower surface of the center platen, and a lower intermediate movable platen disposed between and substantially parallel to the center platen and the lower movable platen, the lower movable platens cooperating with the center platen to define a pair of lower workspaces for objects to be pressed; e. means for supporting the upper and lower movable platens from the framework, the support means including a first upper sprocket wheel mounted for rotation above the upper movable platen, a first lower sprocket wheel mounted for rotation below the lower movable platen, and a first endless chain engaging the first sprocket wheels and secured to the upper and lower movable platens so that the weight of the upper platen is substantially balanced by the weight of the lower platen; f. means for supporting the upper and lower intermediate movable platens from the framework, the support means including a second upper sprocket wheel having a diameter less than that of the first sprocket wheel and adapted to rotate independently of said first sprocket wheel, a second lower sprocket wheel having a diameter less than that of the first lower sprocket wheel and adapted to rotate independently of said first lower sprocket wheel, and a second endless chain engaging the second sprocket wheels and secured to the upper and lower intermediate movable platens so that the weight of the upper intermediate platen is substantially balanced by the weight of the lower intermediate platen; and g. drive means for forcing the upper and lower movable platens and the intermediate platen toward the center platen in sequence to apply substantially the same pressure to objects disposed within the workspaces, irrespective of the weight of the movable platens.