Patent GB-678598-A (GB)
Title: Improvements in or relating to compression testing apparatus
IPC: G01N3/06
Filed: 1950-09-07
Abstract: 678,598. Testing physical qualities of materals; indicating apparatus. DUNLOP RUBBER CO., Ltd., (Dunlop Tire & Rubber Goods Co., Ltd.). Sept. 7, 1950, No. 22029/50. Classes 106(ii) and 106(iv). In apparatus for testing the compressibility of articles, e.g. of rubber, similar to that described in Specification 482,373, comprising two presser members 8, 32, having opposed surfaces adapted to contact opposite sides of an article, one of the presser members is moved relatively to the other, an electrical contact 39 is moved at the same speed, and a second contact 38 is moved at a proportional, slower speed in advance of the first and is stopped when a predetermined datum force is exerted on the article, whereby after a further movement of the movable presser member 8, the contacts engage and complete a circuit which stops the member 8 and locks an indicator 29, 30 which indicates the compressive force exerted on the article above the datum force. General construction. As shown in Figs. 2 and 3, a rubber cushion 31 on a support 32 is compressed by a plate 8 mounted on a vertical arm 10 of a scale mechanism carried in a frame 2 suspended by a sprocket chain 7 operated by an electric motor 3. The scale mechanism comprises also a beam 16, pivotally supported at 17 and carrying adjustable weights 19, which is connected by a spring 21 to a beam 11 pivotally supported at 12 and connected by a link 26 to a known spring scale assembly including a shaft 28 damped by a disc 28a and magnets 28b, and carrying an indicating pointer 29 which moves over a scale 30. The motor 3 also rotates a drum 34 thus winding and unwinding a tape 35 on which is hung a weight 36 carrying the electric contact 38. In operation, the frame 2 is lowered until a datum force of one pound is applied to the cushion. The beam 11 then tilts so that contacts 33, 40 are opened which, through circuits described below, operates an electromagnetic device, Fig. 5, which locks the tape 35 and prevents further downward movement of the contact 38, and also causes the motor to operate at a slower speed such that the plate 8 compresses the cushion at the rate of 25 ins./ minute. While the tape is free, the contact 38 is arranged to be spaced from the contact 39 on the arm 10 by a distance equal to “ of the space between plate 8 and support 32, this spacing being maintained by the relative diameters of the drum 34 and chain sprocket. Thus, these contacts are closed when the cushion has been compressed by “ of its thickness under the datum force whereupon circuits are completed to stop the motor 3 and energize electromagnets 52 which attract a brake disc to lock the pointer shaft 28. These operations are effected earlier under excessive load by the closure of contacts 55, 56 by the beam 11. The plate 8 and frame 2 are raised by reversal of the motor and may be automatically stopped in a pre-selected position by selector switches 78, 79, Fig. 6. Electromagnetic tape lock. The tape 35, Fig. 5, passes between electromagnetic coils 44a and a locking strap 42 attracted thereby, both carried by a pivoted plate 43 having at its free end a contact 46 which normally rests on a fixed contact 48 in the circuit of the coils 44a, Fig. 6. When the motor is reversed after a compression test, the slack in the locked tape is first removed and the tape then raises the plate 43 to open contacts 46, 48 to de-energize the coils and unlock the tape. Circuit details. The motor is operated for down or up movement of the compression plate by buttons 66a or 76a, Fig. 6, which operate respectively relays 67, 77, which close and open contacts such as 67b, 77b to energize motor armature 68 and field windings 69, 78, of opposite polarity, across power supply lines 60, 61. The buttons are mechanically connected to switches 66b, 76b so that operation by a button of one relay automatically de-energizes the other. The motor can be stopped manually by operating mechanically connected switches 81a, 81b and is stopped automatically either by the completion of a circuit for relay 80 which opens contacts 80a, when rotary switch arm 79a on the motor shaft arrives opposite pre-set switch arm 78a, or by the opening of limit switch 82. The opening of contacts 33, 40 removes a negative grid bias on gas-filled tetrode V1 which then conducts thus energizing locking coils 44a and a speed-reducing relay 71 which operates contacts 71a, 71b to reduce the potential applied to motor armature 68 to that across lines 62, 61. The closure of contacts 38, 39 supplies a positive grid bias to a similar tetrode V2 which then energizes pointerlocking coils 52, and a stop relay 75 which opens contacts 75a.