Automatic spraying apparatus for forming hard polyurethane foam coating

An automatic spraying apparatus comprising storage tanks, each storing therein one of at least two liquid components which are mixed to produce hard urethane foam;

• a pump for feeding said each liquid component under pressure;
• a spray gun for mixing said liquid components fed from said pumps and spraying the mixture;
• a means displacing said spray gun in a plane spaced apart from and substantially in parallel with a surface to be sprayed, said means comprising a traverse bar, a carriage having mounted thereon said spray gun and being movably mounted upon said traverse bar, a first motor for moving said carriage along said traverse bar, a second motor for displacing said traverse bar in a direction perpendicular to the axis of the said traverse bar in said plane, a first pulse generator for issueing pulse signals the number of which corresponds to the displacement of said carriage, a second pulse generator for issueing pulse signals the number of which corresponds to the displacement of said traverse bar, a first control means in response to said pulse signals from said first pulse generator for reversing the rotation of said first motor when said carriage arrives at either end of said traverse bar, and a second control means for energizing said second motor at the same time as the rotation of said first motor is reversed and de-energizing said second motor in response to said pulse signals from said second pulse generator when the displacement of said traverse bar after energization of said second motor reaches a predetermined level;
• and a pump control circuit comprising a flow meter for detecting the discharge rate of said each pump, means for combining output signals from said flow meters to produce the sum of the detected discharge rates of said pumps, means for dividing output signals from said flow meters to produce the ratio of the detected discharge ratio of said pumps, a first comparator means for comparing said sum of the detected discharge rates with a predetermined total discharge rate of said pumps, a second comparator means for comprising said ratio of the detected discharge rates with a predetermined ratio of discharge rates of said pumps, and means operating in response to output signals from said first and second comparator means and for controlling the discharge rate of said each pump at a predetermined rate determined from said predetermined total discharge rate and said predetermined discharge ratio.